1. Field of the Invention
The present invention relates to a lamp which has improved efficiency. More specifically, a bulb of the lamp is configured to incorporate parabolic inner surfaces which are coated with an IR reflecting material to reflect emitted infrared rays back to a filament of the lamp, thereby increasing the lighting coefficient of the lamp, and, inherently, its efficiency.
2. Prior Art
Generally, the efficiency of incandescent lamps is less than 15%, with infrared (IR) radiation comprising over 85% of the radiant energy thereof. Even more efficient high-pressure sodium, metal halide and xenon lamps still emit 20%-30% of their total radiant energy as IR. Further, the filaments of lamps and the rods of, and an arc produced by, an arc lamp are usually linear, with such linearity creating a key problem in manufacturing lamps with a proper geometric shape for IR reflection. The substantial degree of IR radiation emitted by the above mentioned lamps not only increases costs for lighting due to inefficiency, but also pollutes our environment.
In the early 1980's, it was determined that IR reflecting material layers coated on an interior bulb surface are able to reflect IR radiation emitted from a filament, back to the filament, heating same and greatly increasing the lighting coefficient of the lamp. The reflecting material layers used in early units, however, could only accommodate temperatures up to 500.degree. C., leading to the development of crystalline substances for use in creating a high temperature filament, typically having the form of a dot.
Next, it was proposed to curve a filament to a plane and to position the filament at the center of a spherical bulb, with a dot to dot symmetry about a center point, making it possible to coat an IR reflecting material layer onto the inner surface of the bulb. However, much of the emitted IR radiation is still not reflected to the filament, inasmuch as a spherical lamp bulb produces non-symmetric reflection, when viewed in light of optical geometry.
To further improve lighting efficiency, a type of halogen tungsten filament incandescent lamp incorporating an IR reflecting material layer has been developed in some countries. In a lamp of this type, a filament is positioned along a major axis of an elliptical bulb, the outer surface of which is coated with an IR reflecting material layer. However, lamps of this type have a decreased useful life because two reflective foci around which IR rays are concentrated are inherently produced, forming two hot spots on the filament. Simultaneously, the many IR rays generated near each of the two ends of the filament cannot be reflected back to the filament. Even spherical or cylindrical bulb embodiments of such lamps still do not afford higher efficiency.